Wellbores are drilled through formations having one or more zones of interest for production of a hydrocarbon resource therethrough. The wellbores may be cased and cemented, particularly where the formation is unconsolidated and may otherwise collapse. In order to effect production of resources such as heavy oil, at a minimum perforations must be made through the casing and cement to provide a fluid path between the formation and the wellbore.
It is well known to use perforating guns to create generally cylindrical holes through the casing, which is typically a metal tubular. The perforations created have a limited size. Further, as a result of detonation of the perforating gun, it has been reported that there may be near wellbore damage resulting in a reduction in rock permeability.
Perforations through casing are also made using abrasive fluid jetting techniques whereby a tool having nozzles therein is deployed into the wellbore. An abrasive fluid is pumped through the tool to exit the nozzles, the fluid being directed against the casing. The abrasive fluid acts to cut the perforations in the casing. The abrasive fluid can be returned to surface through an annulus between the perforating tool and the casing.
It is also well known to use such abrasive jetting techniques to cut axially extending slots through the casing for establishing elongated flow paths between the formation and the wellbore. Applicant believes however that such slots may act to weaken the overall integrity of the casing, resulting in an increased risk of a localized casing failure.
Further, it is also known to use abrasive fluids exiting to cutting perforations in the casing and to penetrate the formation therebeyond for creating production channels in the formation. In U.S. Pat. No. 5,445,220 to Gurevich, a perforator having both telescoping nozzles and double jet nozzles is reciprocated within the wellbore by lifting and lowering the tool from surface, and abrasive fluid is discharged for cutting continuous perforations or slot.
There remains interest in apparatus and methods for forming openings in casing through which effective production paths may be created and for more efficiently and effectively removing near wellbore damage which encourage the flow of hydrocarbons thereto while minimizing risk to the casing structure.